The invention is based on a method of stabilizing the wavelength of lasers and a wavelength monitor for regulating the wavelength of a laser, comprising an optical input, a splitter, a wavelength filter in one branch, and two photodetectors.
Methods of wavelength stabilization are known from the prior art, for example from U.S. Pat. No. 4,583,228. A wave monitor is used in this wavelength stabilization method. Here the light of a laser firstly passes through a beam splitter and strikes a photodetector in each of two branches. One of the two branches contains a Fabry-Perot interferometer. The photocurrents supplied by the two photodiodes are compared in a differential amplifier or divider and supply a resultant error signal required for the control circuit. The wavelength monitor is set at a defined wavelength or group of wavelengths. For this purpose, in one optical branch the Fabry-Perot filter is tuned and in the other optical branch the reference level is set by purposive attenuation of the signal. This known prior art is also described in detail in FIGS. 1 to 3. However, this is an elaborate method and corresponding monitor. Tunable Fabry-Perot filters are mechanically sensitive and cannot be integrated in a module with suitably small structural dimensions.
The advantage of the method according to the invention is that it is easily possible to adapt the monitor to different wavelengths by regulating one of the two photodiodes and by using a specially dimensioned wavelength filter. In particular in a situation in which the spacings between the wavelengths of a wavelength division multiplex become increasingly smaller, the monitor according to the invention is easily adaptable. Here a wavelength filter is used which is not tunable and thus has reduced sensitivity in respect of mechanical problems.